The chemistry of trace metals and oxygen have significant implications in such health related areas as cancer chemotherapy and heart and lung disease. The importance of oxygen binding to various types of heme units in biological molecules is well known especially in regard to O2 transport and the respiratory process. The interaction of manganese with O2 is postulated in such reactions as photosynthetic O2 evolution in chloroplasts and the scavanging of superoxide ion by superoxide dismutase. Being a poorly coordinating trace metal in rather fragile biological systems creates experimental problems regarding the role and nature of manganese. A detailed investigation into the interaction of oxygen with relatively simple manganese coordination compounds is proposed. The research program envisioned is sixfold: (1) Prepare and characterize potential manganese-dioxygen precursors which exhibit a range of stereochemistries, (2) Synthesize and study the oxygenation products of manganese(II) chelates, (3) Establish the mechanism of interaction between manganese complex and dioxygen, (4) Explore the reactivity of other small molecules such as nitric oxide with simple manganese chelates, (5) Determine the oxygenase activity of simple manganese systems and (6) Study the redox properties of manganese compounds as a function of various ligand parameters. Factors to be elucidated include the structural requirements for reversible O2 uptake, the nature of the manganese-oxygen linkage and the role of manganese in photosynthetic O2 evolution and superoxide dismutase.